This invention relates to water-dispersed adhesive compositions and particularly to water-dispersed adhesive compositions that form adhesives that can be thermally activated at low temperatures.
In the manufacture of office or automobile seating, a fabric is typically bonded to a contoured foam surface. The cloth-covered foam may then also be bonded to a support material such as wood or plastic. The contoured foam is typically bonded to the fabric by an adhesive. The adhesive may be applied when the part is needed or may be applied, allowed to dry, and then bonded at a later time depending upon the characteristics of the particular adhesive.
Adhesives such as sprayable hot melts, solvent based adhesives, and water-based contact adhesives have been used for such applications. Sprayable hot melt adhesives typically require specialized spray and storage equipment and have a short open time. Hot melt adhesives may also require re-heating at relatively high temperatures, for example, 265xc2x0 F.-350xc2x0 F. (130xc2x0 C.-177xc2x0 C.) to re-melt the adhesive and form a bond. Solvent-based adhesives are available with a wide range of solvated polymers, including crystallizing polyurethanes. However, the use of materials containing organic solvents in the workplace has raised emission and exposure concerns.
Water-dispersed adhesives are known in the art. These adhesives have gained commercial success in general because they are typically easily applied to substrates and do not contain appreciable amounts of organic solvents.
However, water-dispersed adhesives currently available may not provide adequate adhesion to all substrates. One example of a substrate that can be difficult to bond is flexible foam, in particular, molded foam. Molded foams, typically made using urethanes, are difficult to bond because the surface of the foam is smooth and relatively non-porous and often has mold release residue dispersed about its surface. Such foams are generally more difficult to bond because the combination of a smooth surface and any additional mold-release residue provides a surface that has a lower surface energy than a foam that does not have a molded surface.
In one aspect, the present invention provides low temperature activatable water-dispersed adhesive compositions. The adhesive compositions of the invention comprise low modulus crystallizing polyester polyurethane, acrylic ester copolymer, one or more hydrophobically-modified associative polyurethanes, and a stabilizer system comprising a combination of carbodiimide and branched primary amino alcohol.
In another aspect, the invention provides adhesives made from the adhesive compositions described in this application.
The term xe2x80x9cwater dispersedxe2x80x9d means that the carrier is primarily water. However, incidental organic solvents, such as those present in additives and commercially available components, may be present. Thus, the adhesive compositions of the invention are at least substantially free of organic solvents. Preferably, however, xe2x80x9cwater-dispersedxe2x80x9d refers to a 100% water carrier.
The term xe2x80x9cdispersionxe2x80x9d encompasses any form of solid dispersed in a liquid medium including, for example, latexes, emulsions, colloidal suspensions, and the like.
The adhesive compositions or the adhesives of the invention contain no external plasticizer or zinc oxide. The adhesive compositions of the invention also preferably contain no polychloroprene resins or dispersions.
The term xe2x80x9cplasticizerxe2x80x9d as used herein means compounds from the following classes: phthalates including alkyl benzyl phthalates; adipates including dialkyl adipates; phosphates including alkyl aryl phosphates and triaryl phosphates; alkyl and aryl sulfonamides; and hydrogenated terphenyls.
The term xe2x80x9clow temperature activatable adhesivexe2x80x9d means adhesives of the invention that are capable of bonding substrates at a bondline temperature of as low as 43xc2x0 C.
The term xe2x80x9clow modulusxe2x80x9d means a storage modulus (Gxe2x80x2) not more than 3xc3x97106 dynes/cm2 at 60xc2x0 C., and preferably not more than 1xc3x97109 dynes/cm2 at 20xc2x0 C., as measured by dynamic mechanical analysis (DMA) at a frequency of 1 Hertz.
The term xe2x80x9ccrystallizing polyester polyurethanexe2x80x9d means a polyester polyurethane polymer that has at least one measurable glass transition temperature (Tg) above 20xc2x0 C. as measured by DMA.
The term xe2x80x9cadhesive compositionxe2x80x9d means a mixture of adhesive components dispersed in water. The term xe2x80x9cadhesivexe2x80x9d means a mixture of adhesive components wherein water has been removed.
The adhesives of the invention after coating onto a substrate may be formulated to be non-blocking at ambient temperature (23xc2x0 C.), and then can be thermally activated to form a bond.
The adhesives of the invention also provide open times of at least 3 days at ambient conditions. The term xe2x80x9copen timexe2x80x9d means the time that an effective adhesive bond can still be made, after the adhesive has been applied to a substrate and dried.
Other advantages of the adhesive compositions of the invention include the adhesive compositions are sprayable, can be bonded at low pressures (1-3 psi (0.048-0.14 kPa)), provide high green strength durable bonds, that is, bonds that maintain or increase in bond strength and are environmentally resistant, for example, at 52xc2x0 C. and 80% RH, for 48 hours, the adhesives can be bonded greater than 24 hours after drying (non-blocking), and the adhesive compositions of the invention have low penetration into porous surfaces.
The water-dispersed adhesive compositions of the invention comprise one or more low modulus crystallizing polyester polyurethanes, acrylic ester copolymer, one or more hydrophobically-modified associative polyurethanes, and a stabilizer system. The water-dispersed adhesive compositions optionally, but preferably, contain one or more antioxidants.
Acrylic ester copolymer is generally present in the adhesive compositions of the invention in an amount of from about 60 to about 400 parts per 100 parts low modulus crystallizing polyester polyurethanes on a dry weight basis, or xe2x80x9cphr urethane.xe2x80x9d Acrylic ester copolymer is preferably present in the adhesive compositions of the invention in an amount of from about 70 to about 230 phr urethane and more preferably present in an amount of from about 80 to about 160 phr urethane.
Hydrophobically-modified associative polyurethane is generally present in the adhesive compositions of the invention in an amount of from about 0.05 to about 2, preferably from about 0.07 to about 1, and more preferably from about 0.07 to about 0.5 phr urethane.
The adhesive compositions of the invention contain a stabilizer system. The stabilizer system is a combination of carbodiimide and branched primary amino alcohol. Carbodiimide is present in the adhesive compositions of the invention in an amount of from about 1 to about 8 phr, preferably from about 1.5 to about 7 phr, more preferably from about 2.0 to about 6.5 phr urethane. Branched primary amino alcohol is present in the adhesive compositions of the invention in an amount from about 1.5 to about 7 phr, preferably from about 2 to about 4 phr, more preferably from about 2.3 to about 3.5 phr urethane. Generally, the ratio of carbodiimide to branched primary amino alcohol ranges from about 2 to 0.5 to about 0.5 to 2 by weight with a ratio of about 2 to 1 preferred.
If present, antioxidant is provided in the adhesive composition of the invention in an amount of from about 1.5 to about 7.0, preferably, about 2.0 to about 5.0, more preferably, about 2.4 to about 2.8 phr urethane.
The water-dispersed adhesive compositions of the invention contain one or more low modulus crystallizing polyester polyurethane, preferably in the form of a water dispersion. The low modulus crystallizing polyester polyurethane provides the adhesives of the invention with high hot tack, a rapid crystallization rate resulting in high green strength, a high solids content ( greater than 50%), an extended bond range capability of at least 3 days, and moderate heat resistance. The low modulus crystallizing polyester polyurethane can either be carboxylated or sulfonated, but is preferably carboxylated. Low modulus crystallizing polyester polyurethanes can be generally made by methods described in PCT Publication WO 99/26993. Useful low modulus crystallizing polyester polyurethanes include those having the trade designations Dispercoll(trademark) KA-8756 (Bayer) (Gxe2x80x2 @ 25xc2x0 C.xcx9c1xc3x97109, @ 60xc2x0 C.xcx9c1xc3x97106, @ 80xc2x0 C.xcx9c9xc3x97105 dynes/cm2); Neocryl(trademark) 9617 (Neoresins Division of Avecia Inc.) (Gxe2x80x2 @ 25xc2x0 C.xcx9c1xc3x97108, @ 60xc2x0 C.xcx9c1xc3x97106, @ 80xc2x0 C.xcx9c9xc3x97105 dynes/cm2); and Quilastic(trademark) DEP 170 (Gxe2x80x2 @ 25xc2x0 C.xcx9c1xc3x97109, @ 60xc2x0 C. 1xc3x97106, @ 80xc2x0 C.xcx9c7xc3x97105 dynes/cm2) and Quilastic(trademark) DEP 172 (Merquinsa) (Gxe2x80x2 @ 25xc2x0 C.xcx9c1xc3x97109, @ 60xc2x0 C.xcx9c2xc3x97106, @ 80xc2x0 C.xcx9c2xc3x97106 dynes/cm2). All of the above storage modulus values are measured values using DMA at a frequency of 1 Hertz.
The acrylic ester copolymer enhances hot tack properties of the adhesive and acts as a compatibilizer for the low modulus crystallizing polyester polyurethane and the stabilizer system and other resins. Useful acrylic ester copolymers have a rubbery plateau modulus where the storage modulus (Gxe2x80x2) is not more than 8xc3x97105 dynes/cm2 at 80xc2x0 C. and 1xc3x97106 dynes/cm2 at 50xc2x0 C., and are preferably anionic. General teachings of how such acrylic ester copolymers are made can be found in U.S. Pat. Nos. 4,250,070 and 4,931,494, incorporated by reference herein. Commercially available acrylic ester copolymers useful in the water-dispersed adhesive compositions of the invention include Acronal(copyright) A-310 S (butyl acrylate/methyl methacrylate copolymer dispersion; Tg: xe2x88x9220xc2x0 C.), Acronal(copyright) A-311 (butyl acrylate/methyl methacrylate copolymer dispersion; Tg: xe2x88x9220xc2x0 C.) Acronal(copyright) V210 (vinyl acetate/2-ethylhexyl acrylate/styrene terpolymer dispersion; Tg: xe2x88x9240xc2x0 C.), and Acronal(copyright) DS3505 (butylacrylate/styrene copolymer dispersion; Tg: xe2x88x9235xc2x0 C.), available from BASF Corporation and Rhoplex(trademark) CA-597 (Butyl acrylate/acid component dispersion; Tg: 5xc2x0 C.) (Rohm and Haas). The acrylic ester copolymers having the tradenames Acronal((copyright) A-310 S and A-311 are believed to be derived from a copolymer of butyl acrylate and methyl methacrylate and crosslinked with a dihydrazide.
The hydrophobically-modified associative polyurethanes of the adhesive compositions of the invention function primarily as rheology modifiers and provide a means of formulating to provide rapid recovery from shear thinning after application of the adhesive composition to a substrate. Hydrophobically-modified associative polyurethanes are added to the adhesive compositions so to provide adhesive compositions having near-Newtonian flow characteristics and an effective amount of a hydrophobically-modified associative polyurethane is that amount which provides an adhesive composition of the invention with Newtonian flow characteristics. HEUR (hydrophobically modified ethylene oxide -based urethane resins, a class of hydrophobically-modified polyurethanes), perform independent of adhesive composition pH. The hydrophobe groups interact with the dispersed polymer and any resin particles that are present in the adhesive composition to form weak associative complexes with other hydrophobe groups at the surface of the dispersed polymer particles. Some HEUR are capable of imparting near-Newtonian rheology. Commercially available hydrophobically-modified associative polyurethanes are in the form of dispersions and include those having the tradenames Nopco(trademark) DSX 1514 and 1550 (Henkel Corporation, Ambler, Pa.); Alcogum(trademark) N-300 (Alco Chemical, Chattanooga, Tenn.) and Acrysol(trademark) RM-825, RM 1020, RM 8W (Rohm and Haas).
The adhesive compositions of the invention contain an effective amount of a stabilizer system. An xe2x80x9ceffective amountxe2x80x9d of a stabilizer system means an amount of stabilizer system so to prevent either coagulation of the crystallizing polyester polyurethane or hydrolysis of any ester moieties of the crystallizing polyester polyurethane or other resins containing ester moieties. Hydrolysis of ester moieties of the crystallizing polyester polyurethane will cause the adhesive performance of the adhesive to decline. Such hydrolysis may be detected by a major shift in pH of the adhesive composition and by using analytical techniques such as Fourier Transform Infrared Spectroscopy (FTIR) gas chromatography, and mass spectrometry. The stabilizer systems of the adhesive compositions of the invention protect polyester groups in the polyurethane from hydrolysis in the adhesive composition and the adhesive. The stabilizer system of the adhesive compositions of the invention comprises a combination of branched primary amino alcohol and carbodiimide.
Branched primary amino alcohols act primarily as acid scavengers. The branched primary amino alcohols are derived from nitroparaffins by way of nitro alcohols. Useful branched primary amino alcohols are those which are miscible in water. Preferred branched primary amino alcohols include 2-amino-1-butanol; 2-amino-2-methyl-1,3-propanediol; 2-amino-2-methyl-1-propanol; 2-amino-2-ethyl-1,3-propanediol; and tris(hydroxymethyl)aminomethane and combinations thereof.
A carbodiimide as used herein is a compound containing the functional group: xe2x80x94Nxe2x95x90Cxe2x95x90Nxe2x80x94. The carbodiimides are useful for preventing hydrolysis of functional groups such as ester groups. The carbodiimides may be aliphatic or aromatic. Useful carbodiimides are either miscible or dispersible in water. Preferred carbodiimides are those that are sterically hindered, water miscible, and contain little or no organic solvent. Preferred commercially available carbodiimides include Stabaxol(copyright) P 200 (reaction product of tetramethylxylene diisocyanate; water-dispersed), Stabaxol(copyright) P (poly(nitrilomethanetetraylnitrilo (2,4,6-tris(1-methylethyl)-1,3-phenylene)), and Stabaxol(copyright) I (tetraisopropyldiphenylcarbodiimide) (RheinChemie) and Ucarlnk(copyright) XL-29SE (Union Carbide, Danbury, Conn.). Both Stabaxol(copyright) P and I are useful in the compositions of the invention if first dispersed in water.
The adhesive compositions of the invention preferably, but optionally, contain one or more antioxidants. Useful antioxidants include Octolite(trademark) 640, a 55% by weight solids emulsion blend 50:50 by weight of a polymeric hindered phenol and a thioester; Octolite(trademark) 561, a 50% by weight solids dispersion of 4,4xe2x80x2-butylidenebis(6-t-butyl-m-cresol); Octolite(trademark) 544, a 55% by weight solids dispersion of N,Nxe2x80x2-di-beta-napthyl-p-phenylenediamine; Octolite(trademark) 504, a 50% by weight solids dispersion of 2,2xe2x80x2-methylenebis(6-t-butyl-p-cresol); Octolite(trademark) 485, a 46% by weight solids dispersion of Bisphenol antioxidant, an anionic emulsion of Uniroyal""s Naugawhite Liquid); Octolite(trademark) 424, a 63% by weight solids emulsion blend 50:50 by weight of a polymeric hindered phenol and di-tridecylthiodipropionate (DTDTDP) thioester; Octolite(trademark) AO-50, a 50% by weight solids emulsion of a hindered phenol and DTDTDP thioester; Octolite(trademark) AO-28, a 63% by weight solids emulsion blend 80:20 of a polymeric hindered phenol and DTDTDP thioether; and Octolite(trademark) WL, a 50% by weight solids emulsion of butylated reaction product of para-cresol and dicyclopentadiene, all available from Tiarco Chemical Division, Textile Rubber and Chemical Company, Inc., Dalton, Ga.
The thermal resistance of the adhesives of the invention may be further increased by adding one or more water-dispersed or water dispersible isocyanates to the adhesive compositions of the invention. As used herein xe2x80x9cisocyanatesxe2x80x9d include both blocked and unblocked isocyanates. Examples of useful isocyanates include Desmodur(trademark) DA, KA 8703, and BL-116 (Bayer, Pittsburgh, Pa.); Trixene(trademark) BI 7986 (Baxenden Chemicals, Baxenden, England); and HD-100 (Lyondell Chemical, Newtown Square, Pa.). Generally, if present, isocyanates may be present in the adhesive compositions at levels of about 1 to about 7.5% by dry weight of the water based composition, with a level of from 3 to 5% by dry weight of the composition being preferred. Additionally, water-dispersible dihydrazide containing materials, water-dispersible epoxy resins, and water dispersible silanes may be used to enhance thermal resistance of the adhesives made from the adhesive compositions of the invention.
The water-dispersed adhesive compositions of the invention may also include one or more additional rheology modifiers in addition to hydrophobically-modified associative polyurethanes to control the flow of the adhesive composition. Rheology modifiers are added to the adhesive compositions so to provide adhesive compositions having near-Newtonian flow characteristics and an effective amount of a rheology modifier is that amount which provides an adhesive composition of the invention with near-Newtonian flow characteristics. Useful rheology modifiers include alkali soluble or swellable emulsions such as Acrysol(trademark) ASE-60, ASE-75, and ASE-95NP, Acusol(trademark) 810A (Rohm and Haas) and Alcogum(trademark) L-15, L-131, and L-37 (Alco Chemical), alkali soluble associative emulsions such as Alcogum(trademark) SL-70, and 78 (Alco Chemical) or Acrysol(trademark) TT-935 or RM-5 (Rohm and Haas), and alkali swellable associative urethanes such as Polyphobe(trademark) P-104, and P-106 (Union Carbide, Cary, N.C.), and combinations thereof.
Pigments may be added to color the adhesive compositions. Suitable pigments are available as powders, which are water dispersible, or as aqueous dispersions. Some suitable pigments include Phthalocyanine Green and Blue Pigment aqueous dispersion (Hilton Davis Chemical Co., Cincinnati, Ohio), Akrosperse(trademark) Calcium 2B red aqueous dispersion (Akrochem Corporation, Akron, Ohio), and Carbon Black(trademark) aqueous dispersion (Technical Industries Inc., Peace Dale; R.I.), and combinations thereof.
The adhesive compositions of the invention may also contain other conventional additives such as adhesion promoters. A preferred silane adhesion promoter is Silquest(trademark) Coatosil(trademark) 1770 (beta-(3,4-epoxycyclohexyl)ethyltri-ethoxysilane) or Silquest(trademark) Y-15078 (gamma-glycidoxypropylmethyldiethoxysilane), both available from CK Witco Corporation, Tarrytown, N.Y.
The adhesive compositions of the invention may also contain fillers such as glass or polymeric beads or bubbles (expanded or unexpanded), thermally conductive particles, electrically conductive particles, and the like.
The adhesive compositions can be made by first combining the acrylic ester copolymer with a branched primary amino alcohol and then adding the crystallizing polyester polyurethane, followed by the remaining ingredients. The order is specific because the branched primary amino alcohol acts as a buffer for the lower pH acrylic ester copolymer. Normally, low shear mixing equipment can be used. In the instance where the acrylic ester copolymer does not require buffering, for example, Acronal(copyright) A-310 S, then the acrylic ester copolymer is combined with any optional rheology modifier, and then adding the crystallizing polyester polyurethane, branched primary amino alcohol, and the remaining ingredients.
The adhesive compositions of the invention can be applied to one or both surfaces of the substrates to be bonded. The preferred adhesive compositions are preferably applied to a substrate by spraying. However, adhesive compositions of the invention may also be applied by conventional means, such as brush, paint roller, or roll coater provided that the adhesive composition has the appropriate viscosity. The adhesive compositions of the invention may also be applied to release liners and dried to form self-supporting films that can be die cut into any desired shape. Adhesive compositions of the invention may be dried at room or elevated temperatures.
The adhesive compositions of the invention can also be applied over the same or another applied adhesive so as to form a multilayer construction.
Once the adhesive compositions of the invention have been applied to a substrate and dried, the resulting adhesives of the invention may be bonded by contacting the dried adhesive to another substrate to be bonded (the second substrate coated or not coated with adhesive of the invention) and heating the adhesive to a bondline temperature of at least 43xc2x0 C. and, preferably, from about 45 to about 49xc2x0 C. The bonded assembly is held in place for about 25-45 seconds. Heat may be applied to the adhesive/substrate combination by any means such as hot press, heat gun, heat lamps, oven, conformable heated fluidized bed such as a waterbed or bed of flowable particles, heated bladder press, or a steam press.
Examples of substrates that can be bonded include open and closed cell foams, skin or molded polyurethane foams, wood, fabrics, metals, and plastics. Examples of foams include polyurethanes, polystyrenes, polychloroprenes, and the like. Specific examples of fabrics include those made from acrylics, vinyls, leathers, cottons, nylons, polyesters, rayons, and the like. Specific plastics include polyvinyl chlorides, acrylonitrile/butadiene/styrenes, high impact polystyrenes, and blends thereof containing for example polycarbonates, and the like.